Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described in terms of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart.
Present day cardiac pacemakers are typically designed to be implanted in a "pocket" of fatty tissue near the patient's upper breast or lower abdomen. Accordingly, the electronic circuits within the pacemaker are hermetically sealed within a housing made of a material compatible with body tissue. Electrical connection is made with the pacemaker electronic circuits via feedthrough terminals that pass through the hermetically sealed housing. The feedthrough terminals are electrically connected to a connector receptacle in the pacemaker housing for receiving the proximal end of a pacing lead. The lead has a distal end having electrodes attached to the desired tissue location. For cardiac pacing, such a lead is typically inserted through one of the main veins of the patient, for example, the superior vena cava so that the distal end of the lead is directed inside the heart.
Good electrical contact must be maintained between the proximal end of the pacing lead and the pacing lead receptacle on the pacemaker. Further, the connection must be secure so that it does not come apart during use yet it must be detachable in the event the pacemaker or lead needs to be replaced. Moreover, the connection must at all times remain insulated and sealed from body fluids; such fluids are conductive and could cause an electrical short if permitted to infiltrate the connector assembly.
Multiconductor pacing leads such as coaxial bipolar leads include a pin electrode projecting from the proximal tip or extremity of the lead and one or more proximal ring electrodes. The pin and ring electrodes are designed to make secure electrical contact with mating terminals carried by the pacemaker lead receptacle. Recently, there has been an effort to standardize this interface between the pacing lead and pacemaker. See, for example, Calfee et al., "A Voluntary Standard For 3.2 mm Unipolar and Bipolar Pacemaker Leads and Connectors,"PACE, Vol. 9, pp. 1181-85 (November-December 1986). The standard described therein, now referred to by the designation VS-1 (Voluntary Standard - 1), has been adopted by most pacemaker manufacturers worldwide. Among other things, the VS-1 standard defines and specifies the dimensions of the pacing lead and the pacemaker receptacle into which the proximal end of the pacing lead is inserted. Examples of VS-1 connectors are shown in U.S. Pat. Nos. 5,076,270; 5,012,807; 4,848,346; and 4,934,366.
The very nature of an implantable device makes it desirable, of course, to reduce as much as possible the size of the housing of such a device. The VS-1 standard connector receptacle/pacing lead dimensions are factors which contribute to determining the size of the housing of the implantable medical device. It has now become evident that these standard dimensions place constraints on the ability to reduce the size of the housing. Accordingly, it would be desirable to have a connector assembly that removes the constraints imposed by the VS-1 standard connector assembly dimensions so as to permit the design of more compact implantable medical devices. At the same time, it would also be desirable for the pacing lead comprising part of such an assembly to be adaptable for use with pacemakers having pacing lead receptacles complying with the VS-1 standard.